The molecular basis of alcohol action in the nervous system is poorly understood. Neurotransmitter receptors have been found to be alcohol sensitive membrane proteins. We studied molecular determinants of alcohol sensitivity of these proteins. A nicotinic-serotonergic chimera indicated that the N-terminal domain is involved in the action of ethanol on this protein (Mol Pharmacol 1996;50:1010). We found that site directed mutagenesis of single amino acids in the N-terminal domain of the 5-HT3 receptor alters the ethanol sensitivity of this protein. The wild-type and mutant receptors were expressed in Xenopus oocytes and their function studied using two-electrode voltage-clamp. Substitution of arginine (R) for the 245 alanine (A) [R245A] greatly increased the ethanol sensitivity of the receptor. On the other hand, substitution arginine (R) for the 243 alanine (A) [R243A] decreased the ethanol sensitivity of the receptor. The increased ethanol sensitivity of R245A appears to be associated with an increase in the agonist affinity of the receptor, whereas the decreased ethanol sensitivity of R243A appears to be associated with a decrease in the agonist affinity of the receptor. Experiments are currently in progress using different amino substitutions to study whether there also is an association of ethanol sensitivity with the hydrophobicity, charge or molecular volume of the substituted amino acids. The observations indicate that single amino acids in the molecular structure of a receptor can affect the ethanol sensitivity of the receptor. - neuroscience, alcohol, receptor, ion channel, oocyte, molecular biology, electrophysiology